import { asyncScheduler } from '../scheduler/async';
import { MonoTypeOperatorFunction, SchedulerLike } from '../types';
import { debounce } from './debounce';
import { timer } from '../observable/timer';

/**
 * Emits a notification from the source Observable only after a particular time span
 * has passed without another source emission.
 *
 * <span class="informal">It's like {@link delay}, but passes only the most
 * recent notification from each burst of emissions.</span>
 *
 * ![](debounceTime.png)
 *
 * `debounceTime` delays notifications emitted by the source Observable, but drops
 * previous pending delayed emissions if a new notification arrives on the source
 * Observable. This operator keeps track of the most recent notification from the
 * source Observable, and emits that only when `dueTime` has passed
 * without any other notification appearing on the source Observable. If a new value
 * appears before `dueTime` silence occurs, the previous notification will be dropped
 * and will not be emitted and a new `dueTime` is scheduled.
 * If the completing event happens during `dueTime` the last cached notification
 * is emitted before the completion event is forwarded to the output observable.
 * If the error event happens during `dueTime` or after it only the error event is
 * forwarded to the output observable. The cache notification is not emitted in this case.
 *
 * This is a rate-limiting operator, because it is impossible for more than one
 * notification to be emitted in any time window of duration `dueTime`, but it is also
 * a delay-like operator since output emissions do not occur at the same time as
 * they did on the source Observable. Optionally takes a {@link SchedulerLike} for
 * managing timers.
 *
 * ## Example
 * Emit the most recent click after a burst of clicks
 * ```ts
 * import { fromEvent } from 'rxjs';
 * import { debounceTime } from 'rxjs/operators';
 *
 * const clicks = fromEvent(document, 'click');
 * const result = clicks.pipe(debounceTime(1000));
 * result.subscribe(x => console.log(x));
 * ```
 *
 * @see {@link audit}
 * @see {@link auditTime}
 * @see {@link debounce}
 * @see {@link debounceTime}
 * @see {@link sample}
 * @see {@link sampleTime}
 * @see {@link throttle}
 * @see {@link throttleTime}
 *
 * @param {number} dueTime The timeout duration in milliseconds (or the time
 * unit determined internally by the optional `scheduler`) for the window of
 * time required to wait for emission silence before emitting the most recent
 * source value.
 * @param {SchedulerLike} [scheduler=async] The {@link SchedulerLike} to use for
 * managing the timers that handle the timeout for each value.
 * @return {Observable} An Observable that delays the emissions of the source
 * Observable by the specified `dueTime`, and may drop some values if they occur
 * too frequently.
 */
export function debounceTime<T>(dueTime: number, scheduler: SchedulerLike = asyncScheduler): MonoTypeOperatorFunction<T> {
  const duration = timer(dueTime, scheduler);
  return debounce(() => duration);
}
